Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$50.63	12.370%	$56.8929	$56.89	$56.90	$56.90
Purchase #2	$131.62	9.742%	$144.4424	$144.44	$144.45	$144.40
Purchase #3	$200.30	13.605%	$227.5508	$227.55	$227.55	$227.60
Purchase #4	$228.71	11.662%	$255.3822	$255.38	$255.40	$255.40
Purchase #5	$180.47	11.243%	$200.7602	$200.76	$200.75	$200.80
Purchase #6	$238.85	9.568%	$261.7032	$261.70	$261.70	$261.70
Purchase #7	$161.33	8.250%	$174.6397	$174.64	$174.65	$174.60
7 purchase totals =	$1,191.91		$1,321.3714	$1,321.36	$1,321.40	$1,321.40